1 of 10 022102
FEATURES
§ Upgrade and drop-in replacement for DS2400
— Extended 2.8 to 6.0 voltage range
— Multiple DS2401s can reside on a
common 1-Wireâ Net
§ Unique, factory-lasered and tested 64-bit
registration number (8-bit family code + 48-
bit serial number + 8-bit CRC tester);
guaranteed no two parts alike
§ Built-in multidrop controller ensures
compatibility with other 1-Wire Net
products
§ 8-bit family code specifies DS2401
communications requirements to reader
§ Presence Pulse acknowledges when the
reader first applies voltage
§ Low-cost TO-92, SOT-223, and TSOC
surface mount packages
§ Reduces control, address, data, and power to
a single pin
§ Zero standby power required
§ Directly connects to a single port pin of a
microprocessor and communicates at up to
16.3kbits/s
§ TO-92 Tape & Reel version with leads bent
to 100mil spacing (default) or with straight
leads (DS2401T-SL)
§ Applications
— PCB Identification
— Network Node ID
— Equipment Registration
§ Operates over industrial temperature range of
-40°C to +85°C
PIN ASSIGNMENT
PIN DESCRIPTION
TO-92/SOT-223 TSOC
Pin 1 Ground Ground
Pin 2 Data (DQ) Data (DQ)
Pin 3 No Connect No Connect
Pin 4 Ground No Connect
Pin 5-6 -No Connect
ORDERING INFORMATION
DS2401 TO-92 Package
DS2401Z SOT-223 Surface Mount Package
DS2401/T&R Tape & Reel of DS2401
DS2401T-SL Like DS2401T but Straight Leads
DS2401Z/T&R Tape & Reel of DS2401Z
DS2401P TSOC Surface Mount Package
DS2401P/T&R Tape & Reel of DS2401P
DS2401X1 Chip Scale Pkg., Tape & Reel
DS2401
Silicon Serial Numbe
r
www.maxim-ic.com
TOP VIEW
See Mech. Drawings
Section
TOP VIEW
3.7mm x 4.0mm x 1.5mm
BOTTOM VIEW
TO-92
DALLAS
DS2401
2 3
1
1 2 3
1-Wire is a registered trademark of Dallas Semiconductor.
TSOC PACKAGE
DS2401
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DESCRIPTION
The DS2401 enhanced Silicon Serial Number is a low-cost, electronic registration number that provides
an absolutely unique identity which can be determined with a minimal electronic interface (typically, a
single port pin of a microcontroller). The DS2401 consists of a factory-lasered, 64-bit ROM that includes
a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family Code (01h). Data is transferred serially
via the 1-Wire protocol that requires only a single data lead and a ground return. Power for reading and
writing the device is derived from the data line itself with no need for an external power source. The
DS2401 is an upgrade to the DS2400. The DS2401 is fully reverse-compatible with the DS2400 but
provides the additional multi-rop capability that enables many devices to reside on a single data line. The
familiar TO-92, SOT-223 or TSOC package provides a compact enclosure that allows standard assembly
equipment to handle the device easily.
OPERATION
The DS2401’s internal ROM is accessed via a single data line. The 48-bit serial number, 8-bit family
code and 8-bit CRC are retrieved using the Dallas 1-Wire protocol. This protocol defines bus transactions
in terms of the bus state during specified time slots that are initiated on the falling edge of sync pulses
from the bus master. All data is read and written least significant bit first.
1-WIRE BUS SYSTEM
The 1-Wire bus is a system which has a single bus master system and one or more slaves. In all instances,
the DS2401 is a slave device. The bus master is typically a microcontroller. The discussion of this bus
system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire
signaling (signal type and timing). For a more detailed protocol description, refer to Chapter 4 of the
Book of DS19xx iButton® Standards.
Hardware Configuration
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to
drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have an
open-drain connection or 3-state outputs. The DS2401 is an open-drain part with an internal circuit
equivalent to that shown in Figure 2. The bus master can be the same equivalent circuit. If a bidirectional
pin is not available, separate output and input pins can be tied together. The bus master requires a pullup
resistor at the master end of the bus, with the bus master circuit equivalent to the one shown in Figure 3.
The value of the pullup resistor should be approximately 5kW for short line lengths. A multidrop bus
consists of a 1-Wire bus with multiple slaves attached. The 1-Wire bus has a maximum data rate of
16.3kbits per second.
The idle state for the 1-Wire bus is high. If, for any reason, a transaction needs to be suspended, the bus
MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low
for more than 120ms, one or more of the devices on the bus may be reset.
DS2401 MEMORY MAP Figure 1
8-Bit CRC Code 48-Bit Serial Number 8-Bit Family Code (01h)
MSB LSB MSB LSB MSB LSB
iButton is a registered trademark of Dallas Semiconductor.
DS2401
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DS2401 EQUIVALENT CIRCUIT Figure 2
BUS MASTER CIRCUIT Figure 3
A) Open Drain
Note:
Depending on the 1-Wire communication speed and the bus load characteristics, the optimal pullup
resistor (RPU) value will be in the 1.5kW to 5kW range.
To data connection
of DS2401
B) Standard TTL
To data connection
of DS2401
See note
See note
DS2401
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TRANSACTION SEQUENCE
The sequence for accessing the DS2401 via the 1-Wire port is as follows:
§ Initialization
§ ROM Function Command
§ Read Data
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a reset pulse transmitted by the bus master followed by a Presence Pulse(s) transmitted by the
slave(s).
The Presence Pulse lets the bus master know that the DS2401 is on the bus and is ready to operate. For
more details, see the 1-Wire Signaling section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the four ROM function commands. All
ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure
4):
Read ROM [33h] or [0Fh]
This command allows the bus master to read the DS2401’s 8-bit family code, unique 48-bit serial
number, and 8-bit CRC. This command can only be used if there is a single DS2401 on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (open drain will produce a wired-AND result). The DS2401 Read ROM function will occur with a
command byte of either 33h or 0Fh in order to ensure compatibility with the DS2400, which will only
respond to a 0Fh command word with its 64-bit ROM data.
Match ROM [55h] / Skip ROM [CCh]
The complete 1-Wire protocol for all Dallas Semiconductor iButtons contains a Match ROM and a Skip
ROM command. (See the Book of DS19xx iButton Standards.) Since the DS2401 contains only the 64-bit
ROM with no additional data fields, the Match ROM and Skip ROM are not applicable and will cause no
further activity on the 1-Wire bus if executed. The DS2401 does not interfere with other 1-Wire parts on a
multidrop bus that do respond to a Match ROM or Skip ROM (for example, a DS2401 and DS1994 on
the same bus).
Search ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the 1-
Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process
of elimination to identify the 64-bit ROM codes of all slave devices on the bus. The ROM search process
is the repetition of a simple 3-step routine: read a bit, read the complement of the bit, then write the
desired value of that bit. The bus master performs this simple 3-step routine on each bit of the ROM.
After one complete pass, the bus master knows the contents of the ROM in one device. The remaining
number of devices and their ROM codes may be identified by additional passes. See Chapter 5 of the
Book of DS19xx iButton Standards for a comprehensive discussion of a ROM search, including an actual
example.
DS2401
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1-WIRE SIGNALING
The DS2401 requires a strict protocol to ensure data integrity. The protocol consists of four types of
signaling on one line: reset sequence with Reset Pulse and Presence Pulse, write 0, write 1, and read data.
All these signals except Presence Pulse are initiated by the bus master.
The initialization sequence required to begin any communication with the DS2401 is shown in Figure 5.
A reset pulse followed by a Presence Pulse indicates the DS2401 is ready to send or receive data given
the correct ROM command.
The bus master transmits (TX ) a reset pulse (tRSTL , minimum 480ms). The bus master then releases the
line and goes into receive mode (RX ). The 1-Wire bus is pulled to a high state via the 5kW pullup resistor.
After detecting the rising edge on the data pin, the DS2401 waits (tPDH, 15-60ms) and then transmits the
Presence Pulse (tPDL, 60-240ms). The 1-Wire bus requires a pullup resistor range of 1.5kW to 5kW,
depending on bus load characteristics.
READ/WRITE TIME SLOTS
The definitions of write and read time slots are illustrated in Figure 6. All time slots are initiated by the
master driving the data line low. The falling edge of the data line synchronizes the DS2401 to the master
by triggering a delay circuit in the DS2401. During write time slots, the delay circuit determines when the
DS2401 will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay circuit
determines how long the DS2401 will hold the data line low overriding the “1” generated by the master.
If the data bit is a 1, the DS2401 will leave the read data time slot unchanged.
DS2401
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ROM FUNCTIONS FLOW CHART Figure 4
DS2401
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INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 5
480ms £ tRSTL < ¥ *
480ms £ tRSTH < ¥ (includes recovery time)
15ms £ tPDH < 60ms
60ms £ tPDL < 240ms
* In order not to mask interrupt signaling by other devices on the 1-Wire bus, tRSTL + tR should always
be less than 960ms.
READ/WRITE TIMING DIAGRAM Figure 6
Write-One Time Slot
60ms £ tSLOT < 120ms
1ms £ tLOW1 < 15ms
1ms £ tREC < ¥
RESISTOR
MASTER
RESISTOR
MASTER
DS2401
DS2401
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READ/WRITE TIMING DIAGRAM (cont’d) Figure 6
Write-zero Time Slot
60ms £ tLOW0 < tSLOT < 120ms
1ms £ tREC < ¥
Read-data Time Slot
60ms £ tSLOT < 120ms
1ms £ tLOWR < 15ms
0 £ tRELEASE < 45ms
1ms £ tREC < ¥
tRDV = 15ms
tSU < 1ms
CRC GENERATION
To validate the data transmitted from the DS2401, the bus master may generate a CRC value from the
data as it is received. This generated value is compared to the value stored in the last 8 bits of the
DS2401. If the two CRC values match, the transmission is error-free.
The equivalent polynomial function of this CRC is: CRC = x8 + x5 + x4 + 1. For more details, see the
Book of DS19xx iButton Standards.
CUSTOM DS2401
Customization of a portion of the unique 48-bit serial number by the customer is available. Dallas
Semiconductor will register and assign a specific customer ID in the 12 most significant bits of the 48-bit
field. The next most significant bits are selectable by the customer as a starting value, and the least
significant bits are non-selectable and will be automatically incremented by one. Certain quantities and
conditions apply for these custom parts. Contact your Dallas Semiconductor sales representative for more
information.
RESISTOR
MASTER
DS2401
DS2401
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ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground -0.5V to +7.0V
Operating Temperature Range -40°C to +85°C
Storage Temperature Range -55°C to +125°C
Soldering Temperature See J-STD-020A Specification
* This is a stress rating only and functional operation of the device at these or any other conditions above
those indicated in the operation sections of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods of time may affect reliability.
DC ELECTRICAL CHARACTERISTICS (-40°C to +85°C; VPUP = 2.8V to 6.0V)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Logic 1 VIH 2.2 VCC +0.3 V 1,6
Logic 0 VIL -0.3 +0.8 V 1, 11
Output Logic Low @ 4 mA VOL 0.4 V 1
Output Logic High VOH VPUP 6.0 V 1,2
Input Load Current IL5mA3
Operating Charge QOP 30 nC 7,8
CAPACITANCE (tA = +25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
I/O (1-Wire) CIN/OUT 800 pF 9
AC ELECTRICAL CHARACTERISTICS (-40°C to +85°C; VPUP = 2.8V to 6.0V)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Time Slot tSLOT 60 120 ms
Write 1 Low Time tLOW1 115
ms13
Write 0 Low Time tLOW0 60 120 ms
Read Data Valid tRDV 15 ms12
Release Time tRELEASE 015 45 ms
Read Data Setup tSU 1ms5
Recovery Time tREC 1ms
Reset Time High tRSTH 480 ms4
Reset Time Low tRSTL 480 960 ms10
Presence Detect High tPDH 15 60 ms
Presence Detect Low tPDL 60 240 ms
DS2401
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NOTES:
1) All voltages are referenced to ground.
2) VPUP = external pullup voltage.
3) Input load is to ground.
4) An additional reset or communication sequence cannot begin until the reset high time has expired.
5) Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit. Data is
guaranteed to be valid within 1ms of this falling edge and will remain valid for 14ms minimum (15ms
total from falling edge on 1-Wire bus).
6) VIH is a function of the external pullup resistor and the VCC supply.
7) 30 nanocoulombs per 72 time slots @ 5.0V.
8) At VCC = 5.0V with a 5kW pullup to VCC and a maximum time slot of 120ms.
9) Capacitance on the I/O pin could be 800pF when power is first applied. If a 5kW resistor is used to
pullup the I/O line to VCC, 5ms after power has been applied the parasite capacitance will not affect
normal communications.
10) The reset low time (tRSTL) should be restricted to a maximum of 960ms, to allow interrupt signaling,
otherwise it could mask or conceal interrupt pulses if this device is used in parallel with a DS2404 or
DS1994.
11) Under certain low voltage conditions, VILMAX may have to be reduced to as much as 0.5V to always
guarantee a Presence Pulse.
12) The optimal sampling point for the master is as close as possible to the end time of the tRDV period
without exceeding tRDV. For the case of a Read-One Time slot, this maximizes the amount of time for
the pullup resistor to recover to a high level. For a Read-Zero Time slot, it ensures that a read will
occur before the fastest 1-Wire device(s) releases the line.
13) The duration of the low pulse sent by the master should be a minimum of 1µs with a maximum value
as short as possible to allow time for the pullup resistor to recover the line to a high level before the 1-
Wire device samples in the case of a Write-One Time or before the master samples in the case of a
Read-One Time.
